Alkaline primary cell



June 21, 1949. s, RUBEN 2,473,546

ALKALINE PRIMARY CELL Filed Jan. 23, 1943 245651624750 JHEET HTTRNEYSPatented June 2l, 1949 UNITED STATES PATENT OFFICE ALKALINE PRIMARY CELLSamuel Ruben, New Rochelle, N. Y.

Application January '23, 1943, Serial No. 473,320

16 Claims. 1

This invention relates to primary cells.

An object of the invention is to improve primary cells and dry cells.

Another object is to improve the life of a primary cell under adverseconditions.

Other objects of the invention will be apparent from the description andclaims.

In the drawings:

Figure 1 shows an electrode assembly for a primary cell in the processof assembly;

Figure 2 shows a terminal member for the c'ell;

Figure 3 is a sectional elevation of a completed cell;

Figure 4 shows a multi-cell battery, and

Figure 5 is a graph containing curves showing the voltage output of acell of the present invention compared with that of a cell of the priorart.

The present invention comprises an improvement on the primary cellsdescribed in my prior copending applicationsv Serial No. 456,160 filedAugust 26, 1942 which has become abandoned and Serial No. 468,386 ledDecember 9, 1942.

In my application, Serial No. 456,160 which has become abandoned, ofwhich the present application is a continuation-in-part, I describeaprimary cell comprising a zinc foil anode, a cathode comprising a steelfoil coated with a depolarlzing composition such as cupric oxide,sulphides of copper, lead sulphides or oxides and the like, asemi-permeable member interposed between the foil electrodes and analkaline electrolyte.

In my co-pending application, Serial No. 468,386 (now U. S. LettersPatent 2,463,565), I describe a primary cell comprising a zinc foilanode, a cathode comprising a steel foil coated with a depolarizingcomposition such as cupric oxide, sulphides of copper, lead sulphide oroxide and the like, a spacer between the electrodes and an electrolytecomprising a concentrated alkali metal hydroxide containing water ofhydration.

The invention contemplates a primary electric cell having electrodes ofzinc or the like and a depolarizer formed of a mercury compound such asmercurio oxide with an alkaline electrolyte such as potassium hydroxide.The electrodes may be of large surface area and closely spaced, beingseparated by a spacer comprising a semi-permeable membrane. For usewhere high temperatures are encountered, such as in the tropics or formaximum shelf life, the electrolyte is preferably a solid crystallinematerial containing water of hydration. For low temperature operationthe electrolyte may be a liquid of such high concentration as to preventfreezing at the lowest operating temperature.

Heretofore pri-mary cells have rbeen produced using alkalineelectrolytes such as potassium and sodium hydroxide as liquid solutions.These have always required careful handling and sealing in order toprevent loss of the electrolyte. Moreover, such primary cells weresubject to rapid deterioration at elevated temperatures due toaccelerated attack on the electrodes by the electrolyte. Zinc iscommonly used as one electrode in such cells and it is quite susceptibleto attack by liquid alkaline solutions.

Depolarizing electrodes for such cells have been formed either of porouscarbon or of cupric oxide.l The porous carbon type depends upon air fordepolarizing effect. The cupric oxide type is not dependent upon air andpermits a relatively high current capacity for a given volume of cell.However, when the cell is left on open circuit, trouble results due tosome of the copper compound dissolving in the electrolyte and migratingto the zinc electrode where copper is deposited, setting up localelectrochemical action and causing rapid dissolution of the zincelectrode. This action is much accelerated when the temperature of thecell is increased. For this reason such cells have heretofore not beenfound satisfactory where they were required to be stored or left on opencircuit for any extended period of time and it has been also necessaryto space the zinc and copper compound electrodes rather far apart.

In the prior art in the so-called dry cells the electrolyte is a liquidbut is prevented from running out of the cell by being absorbed in aporous solid such `as paper, carbon, manganese dioxide or finely dividedinert porous materials. However, the electrolyte remains as a liquidwhen absorbed in these media. Its chemical and corrosive action at hightemperatures, resulting in a deterioration of the cells, is not reduced.Electrolytes have also been immobilized by the addition of agelatinizing agent such as starch but this likewise has not reduced thechemical shelf action or deterioration at elevated temperatures.

As described in my copending application Serial No. 456,160, which hasbecome abandoned, I have found that the use of a. senil-permeablemembrane between the electrodes materially reduces local chemical orelectro chemical action and improves the shelf life as well as theoperating life of the cells.

As described in my other copending application Serial No. 468,386, Ihave found that the life of such primary cells or dry cells can befurther increased so as to produce good open circuit life even atelevated temperatures such as are encountered in the tropics, by usingsolid crystalline alkaline electrolytes containing water of hydration.The solid electrolyte helps to prevent migration of copper compoundswhich would otherwise attack the zinc electrode and also, because of itssolid nature, does not itself as readily attack either the zinc orcopper oxide electrodes when the cell is on open circuit. Another andimportant factor is the hygroscopic nature of solid potassium hydroxidewhich eliminates loss of moisture inherent in immobilized liquidelectrolytes.

While cells of both the types described in my prior applications showeda marked improvement over commercial cells of the prior art, I have nowdiscovered that a further improvement can be obtained and a cell havingmuch longer life at elevated temperatures produced by using adepolarizing electrode of a mercury compound, preferably mercuric oxide,instead of the copper oxide used in the prior cells. It has been found,for example, that cupric oxide is somewhat soluble in the electrolytessuch as potassium hydroxide and some dissolution takes place duringimpregnation of the cell unit by the hot liquid alkaline electrolyte.While the use of a semipermeable membrane and the use of an electrolytewhich is solid at temperatures encountered during use will substantiallyprevent migration of the dissolved copper compound to the zinc whereinternal battery action can take place causing deterioration, I have nowfound that the use of a mercury compound increasees the life of suchcells still further. I believe this is due in a large part to the factthat mercury compounds are insoluble in the alkaline electrolytes and donot deposit reduction products on the zinc which cause local action.

Mercurio oxide is the preferred material.

Since this oxide is a poor conductor of electricity in its pure state,it is combined or mixed with a nely divided conductor such as graphiteand bonded as a layer on a conductive backing such as metal foil.

Used in this manner I have found that the cell has a further improvementover those using cupric oxide as a depolarizer in having a higher outputvoltage. The open circuit voltage of a cell having a zinc electrode, apotassium hydroxide electrolyte, and a mercuric oxide-graphitedepolarizer is approximately 1.4 volts as compared to 1.06 volts for acell using a cupric oxide depolarizer.

Referring to the drawing, Figure 1 illustrates the preferred electrodeassembly of a dry cell of my invention. A thin strip of a suitableferrous material such as sheet iron or steel I I coated with the mercurycompound I is welded at one end to a steel rod I0 and then two or threeturns of the sheet are wrapped tightly around the rod. A spacer assemblycomprising a layer I3 of 1.5 mil thick glycerine free regenerated sheetcellulose interposed between two layers 14 of 1 mil Dexter paper is thenlaid on the unwound portion of the steel strip and a strip of 2 to 3 milzinc foil I2 which is to comprise the zinc electrode of the cell is laidon top of this spacer assembly. A second spacer assembly formed in thesame manner of a layer of regenerated sheet cellulose [3a between twopaper layers Ila is then laid on top of the zinc foil and the entireassembly is then wound into a roll wherein the coated steel sheet II isseparated from the zinc foil I2 by the spacer as- 4 semblies ofregenerated sheet cellulose and paper. The paper and regeneratedcellulose strips are at least $4; inch wider than the steel strip andthe zinc foil so that they project slightly beyond the electrodes ateach end to afford adequate separation at the ends of the roll. Thespacer layers arev somewhat longer than the steel strip so that theyextend beyond its end when the roll is wound up but the zinc foil stripextends beyond the spacers so as to form a final turn of zinc foil onthe outside of the roll.

Before proceeding with the description of the cell, the mercury compoundcoating I5 will be described in greater detail. The composition may beformed by milling together red mercuric oxide mixed with 1 to 15%(preferably 3%) of micronized graphite of extremely small particle size,such as 5 to 9 microns, and a 10% solution of polymerized vinyl chloridein a solvent, such as an ether. 46 grams of the powder mixture to 30grams of solution makes a suitable composition. The resultingcomposition is applied by spraying or painting to both surfaces of steelsheet Il after it has first been given a matte surface by Sandblastingor other methods. Sheet II may suitably be formed of steel 2 mils thick.A preferred thickness for the coat is about 2.75 mils on each side ofthe steel backing. After drying. the coating is baked at a temperatureof 130 C. for several hours. The coated steel strip may then be rolledbetween steel rollers such as those used for rolling metal stock. Thisincreases the density and conductivity of the coating, giving it asmooth uniform surface. The rolling is done at a relatively hightemperature such as around 125 C.

A terminal for the zinc electrode is constructed as shown in Figure 2 byApreparing a cylinder I6 from zinc foil and welding a terminal strip Ilto the side of the cylinder at I8 by spot Welding. The weld also unitesthe ends of the foil comprising cylinder I6.

Terminal I'l is preferably formed of a at strip of cadmium metal. I havefound that during impregnation of the cell with an alkaline hydroxideelectrolyte a certain amount of the electrolyte always remains on theterminal and it is very difficult to completely remove it from theprojecting portion of the terminal which extends outside the cell. Ifthis terminal is formed of zinc this has resulted in corrosion of theprojecting portion of the terminal. I have found that cadmium metal isnot subject to this a1- kali corrosion.

After the electrode assembly is wound as described in connection withFigure 1, it is inserted, while still dry, inside cylinder I6 comprisingpart of the terminal assembly of Figure 2 so that the outer turn of thezinc foil electrode I2 engages the inside of cylinder I6. The dimensionsare suitably chosen so that insertion may be made resulting in a rm butnot extremely tight t.

The electrode-terminal assembly thus formed is then impregnated with thealkali metal hydroxide electrolyte. The electrolyte is preferably asolution of potassium hydroxide. Where the cell is to be used in hightemperatures such as in the tropics or in certain industrialapplications and for maximum shelf life at ordinary temperatures Iprefer. to use an electrolyte formed of 340 grams of C. P. KOH(containing 13 to 14% water) in 100 milliliters of water. For normal usean electrolyte formed of 300 grams C. P. KOH to mllliliters of water issatis- 5 factory, and where low temperatures are to be encountered 50 to150 grams C. P. KOH per 100 milliliters of water is used depending onthe temperature to be encountered. For example, 50 grams potassiumhydroxide per 100 milliliters of water provides an electrolyte whichwill operate at temperatures as low as 60 below zero centigrade.Concentrations of potassium hydroxide above 160 grams C. P. KOH per 100milliliters of water will solidify when cooled to room temperature, Itis necessary to heat the solution to about 120 C. to dissolve all thehydroxide where the higher concentrations are used. While otherconcentrations of electrolyte may be used, the preferred range fordry-cells having a solid electrolyte is between 160 and 400 grams C. P.KOH per 100 milliliters of water. For absorbed type dry cells where theelectrolyte remains as a liquid absorbed in the spacers the preferredrange is 25 to 160 grams C. P. KOH.

The cell assembly which has been produced in the manner above describedis heated to about 100 C. and immersed at this temperature in the hotliquid electrolyte and a partial vacuum (such as a reduction in pressureto 5 cm. of mercury) is preferably applied to improve the i'rnpregnationof the space between the electrodes and the absorption of theelectrolyte into the spacers.

After a Vacuum has been applied to remove all the air from theelectrode-spacer assembly, I prefer to apply a pressure of about 100pounds per square inch while the assemblies are still immersed in theliquid electrolyte and to maintain this temperature until thetemperature of the electrolyte has dropped to about 80 C.

The impregnated assemblies are then removed from the electrolyte and theexcess electrolyte is then wiped off. During impregnation the spacersswell considerably during absorption of the electrolyte and develop ahigh pressure between the outer turn of zinc foil and the terminalcylinder i6 producing perfect contact between the electrode andcylinder.

The cell assemblies are then inserted in Pliofilm tubes I9 (see Figure3). Tubes I9 are either molded of Pliofilm or formed from sheet Pliolmwhich can be readily heat welded. The bottom of said tubes is closed.The Pliofllm washer 2d is then inserted over the center electrode l andagainst the top of the roll and a small rubber sleeve 2l is pressed downover the terminal IEI to hold the washer down. A layer of insulatingpitch 22 such as gilsonite is then poured into the top of tube I9 toseal the cell. This results in the completed cell 9 shown in Figure 3.

Any number of such cells may be connected in series to form a drybattery if desired, one form of battery construction being shown inFigure 4. This comprises an inside waxed cardboard box 23 containingpartitions 24 defining spaces into which the cells 9 are inserted. Thecadmium terminal il of each cell is then soldered to the steel terminalIll of the next adjacent cell so as to connect all the cells in seriesand a layer 25 of pitch is poured over the tops of the cells to coverthe terminals. A battery terminal wire 26 is soldered to the terminal I0of the end cell of the series and a terminal wire 21 is soldered to thecadmium terminal Il at the other end of the series. 'Ihe battery thusproduced may then be included in an outer protective cardboard box 28having flaps 29 which fold down over the top of the battery and havesuitable notches or open- 6 ings through which the battery terminalwires extend.

Figure illustrates the comparative performance of a cell of the presentinvention and a cell oi' the prior art, namely an American standard Acell. The curve 30 shows the voltage output of a zinc-KOH-HgO cell at C.through a 22 ohm load. The cell had an electrode area of 1l squareinches, the cell dimensions being inch in diameter and having anelectrode 1%. inch wide. The electrolyte used was formed from 340 gramsKOH to 100 milliliters of water. Curve 3l shows for comparison thevoltage output of a standard A cell which is inch in diameter and 1%inches in height. It will be' noted that the potential of the A cellfalls below 1 volt after slightly less than 3 hours of operation, whilethe voltage of the cell of the present invention remains well above 1volt for more than 'l1/2 hours. It should also be noticed in comparingthe performance of these cells that the A cell is 1% inches long orapproximately twice the length of the cell of my invention so that the Acell requires about twice the space of the cell of the presentinvention.

The comparative performance illustrated in Figure 5 is, of course, theinitial perfomance of both cells. The difference in performance is evenmore marked after a period of shelf life.

While mercurio oxide (red) is the preferred mercury compound for thedepolarizing electrode, other mercury compounds such as mercurous oxide(black) and mercurio sulfide and selenide can be used but are not aseffective.

While nely divided graphite is the preferred conductive material whichis mixed with the mercury compound, other nely divided conductors may beused such as carbon in its various forms, powdered metals of certainkinds, and finely powdered conductive compounds such as cadmium oxide,for example.

Zinc is the preferred electrode material for the negative electrode butit is also possible to use cadmium or an alloy of zinc and cadmium suchas zinc cadmium 30%. The terminal for the zinc electrode may be cadmium,cadmium plated zinc, magnesium or other metal resistant to alkalies andhaving a low potential diiference in respect to zinc.

Potassium hydroxide is the preferred electrolyte material as itmaintains a lower resistance, especially in the solid crystalline form.However, other alkaline electrolytes such as sodium hydroxide andlithium hydroxide may be used in some cases.

Parchmentized paper or other semi-permeable membranes which are notstrongly attacked by the alkaline electrolyte may be substituted for theregenerated sheet cellulose. However, regenerated sheet cellulose is themost satisfactory and greatly reduces the danger of a short circuit. Inthis connection it will be noted that there is substantially no tendencytoward migration of mer cury compounds in solution as they aresubstantially insoluble in the electrolyte. However, the semi-permeablemembrane is still of importance in preventing short circuits by liquidmercury or mercural compounds developed during operation of the cell.Migration of the mercury or mercury compounds to the zinc is not initself harmful in this case as mercury will form an amalgam with thezinc and will not set up an excessive internal battery action.

The cells of the present invention may be used individually or assembledas batteries for general purposes including use in radio sets, ashlights.

hearing aids and the like. They are also sintable for grid bias cells incircuits of the type shown and described in my Patent No. 2,063,524issued December 8, 1936, relating to an electric amplifier circuit. Forcells of this type the depolarizer may be made by pressing the mercuricoxide-graphite mixture into pellet or wafer form, preferably incombination with an iron electrode backing member.

While specific embodiments of the invention have been described, it isintended to cover the invention broadly within the spirit and scope ofthe appended claims.

What is claimed is:

l. A primary cell comprising a sheet metal electrode of metal selectedfrom the group consisting of zinc. cadmium, and their alloys, an alkalimetal hydroxide electrolyte and a depolarizing electrode spaced fromsaid sheet metal electrode and comprising a conductive sheet of aferrous material and a mixture of a finely divided conductive materialand a compound of mercury with an element from the group consisting ofoxygen, sulfur and selenium bonded as a thin conductive surface 3. Aprimary cell comprising a sheet zinc elec- I trode, an alkali metalhydroxide electrolyte and a sheet depolarizing electrode spaced fromsaid zinc electrode and comprising a conductive sheet base of a ferrousmaterial and a coating bonded thereto comprising mercuric oxide and 1 to15% of finely divided graphite.

4. A primary cell comprising a sheet zinc electrode, an alkali metalhydroxide electrolyte and a sheet depolarizing electrode spaced fromsaid zinc electrode and comprising a steel sheet base and a coatingbonded thereto comprising mercuric oxide and 1 to 15% of finely dividedgraphite.

5. A primary cell comprising a zinc sheet electrode, an electrolyte ofpotassium hydroxide and water and a sheet depolarizing electrode spacedfrom said zinc electrode and formed of a conductive sheet base of aferrous material and a coating bonded thereto comprising mercuric oxideas the active depolarizer and 1 to 15% of finely divided graphite toincrease the conductivity of the mixture.

6. A primary cell comprising a zinc sheet electrode, an electrolyte ofpotassium hydroxideand water and a sheet depolarizing electrode spacedfrom said zinc electrode and formed of a steel sheet base and a coatingbonded thereto comprising mercuricoxide as the active depolarizer and 1to of finely divided graphite to increase the conductivity of themixture.

7. A primary cell comprising, in combination, a sheet zinc electrode, asheet depolarizing electrode in closely-spaced parallel relationthereto, a semi-permeable membrane interposed therebetween and analkaline electrolyte contacting said electrodes and impregnating saidmembrane, said depolarizing electrode comprising a conductive sheet of aferrous material and a coating thereon containing mercuric oxide as theactive depolarizing ingredient and a ilnely divided conductive materialmixed therewith to increase the electrode conductivity.

8. A primary cell comprising, in combination, a sheet zinc electrode, asheet depolarizing electrode in closely-spaced parallel relationthereto, a semipermeable membrane interposed therebetween and analkaline electrolyte contacting said electrodes and impregnating saidmembrane, said depolarizing electrode comprising a steel sheet and acoating thereon containing mercuric oxide as the active depolarizingingredient, finely divided graphite mixed therewith to increase the.coating conductivity and an alkali insoluble binder.

9. A primary cell comprising, in combination, a sheet zinc electrode, asheet depolarizing electrode, a semi-permeable membrane and at least onelayer of fibrous material interposed therebetween. and an alkalineelectrolyte impregnating said membrane and fibrous layer, saiddepolarizing electrode comprising a metal backing oi a ferrous materialand a depolarizing layer bonded thereto comprising a mixture of mercuricoxide, 1 to 15% of ilnely divided graphite and a binder,

' said mercuric oxide being the active depolarizing agent and saidgraphite increasing the electrical conductivity of said depolarizinglayer.

10. A primary cell comprising, in combination, an electrode layer formedfrom a metal selected from the group consisting of zinc and cadmium, adepolarizing layer closely spaced in face to face relation thereto, anda solid crystalline alkali metal hydroxide electrolyte containing waterof hydration between said layers and in contact therewith, saiddepolarizing layer comprising mercuric oxide as the active depolarizingingredient and iinely divided graphite mixed therewith to increase theconductivltsr of said laver.

ll. A primary cell comprising, in combination, an electrode layer formedfrom a metal selected from the group consisting of zinc and cadmium, adepolarizing layer closely spaced in face to face relation thereto, anda solid crystalline alkaline electrolyte between said layers and incontact therewith, said depolarizing layer comprising mercuric oxide asthe active depolarizing ingredient and finely divided graphite mixedtherewith to increase the conductivity of said layer, said electrolytebeing formed of potassium hydroxide and water of hydration.

12. A primary cell comprising, in combination, a sheet zinc electrode, asheet depolarizing electrode, a semi-permeable barrier membraneinterposed therebetween, and a solid alkaline electrolyte impregnatingsaid membrane and between said membrane and said electrodes, saidmembrane being substantially insoluble in said electrolyte, saiddepolarizing electrode comprising a conductive sheet of a ferrousmaterial coated with a mixture of mercuric oxide as the activedepolarizing ingredient and graphite mixed therewith to increase theconductivity thereof.

13` A primary cell comprising spaced parallel electrodes of zinc and ofsteel coated with a depolarizing composition of mercuric oxide, graphiteand an alkali-insoluble binder, and a spacer between said electrodescomprising a semi-permeable membrane, and an electrolyte impregnatingsaid spacer and composed of potassium hydroxide and water.

14. A depolarizing electrode for a dry cell comprising a thin sheet of aconducting metal base of a ferrous material coated with a mixture of acompound of mercury combined with an elem'ent selected from the groupconsisting of oxygen, sulfur and selenium as the active depolarizingingredients, a finely divided conductive material to increase theconductivity thereof and y a binder.

15. A primary cell comprising a sheet zinc 5 electrode, a sheetdepolarizing electrode and sheet spacers wound together into a roll withsaid spacers interposed between said electrodes, said spacers comprisingassemblies of a semi-permeable membrane and at least one brous layer,and an electrolyte of potassium hydroxide and water impregnating saidspacers, said depolarizing electrode comprising a conductive sheet of aferrous material coated with a depolarizing composition comprisingmercurio oxide as the active depolarizing agent, graphite mixedtherewith to improve the conductivity and a binder which is insoluble insaid electrolyte.

16. A cathode for dry primary cells comprising a base of ferrous m'etal,and a depolarizer layer compressed on and bonded to said base. saidlayer consisting of an intimate mixture of an oxide of mercuryconstituting the depolarizing agent and of an inert conductive materialfor increasing the conductivity of the layer.

` SAMUEL RUBEN.

10 REFERENCES crrnn The following references are of record in the le ofthis patent:

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